A typical power amplifier includes one or more transistor stages. Each transistor stage supplies excitation to an input signal from a signal source in order to amplify the input signal and provide the amplified signal to a next transistor stage or a receiver.
In order to efficiently transfer the input signal from the signal source to the output transistor stage of a power amplifier, the input impedance of the output transistor stage needs to closely match the impedance of the signal source. The input impedance to each transistor stage of a power amplifier, however, is typically very small and difficult to match.